The present invention relates to valves, and in particular to microelectromechanical systems (MEMS) thermopneumatic valves.
Micromachined valves are known. Many of these valves have used high modulus materials such as silicon or metal for the valve membrane due to process and integration issues.
Silicon membranes have limited realizable deflections. Accordingly, many microvalves using silicon membranes are restricted to low flow applications unless very large membranes are used. These valves have needed to generate a significant amount of force to deflect the silicon membrane properly.
The present invention provides a technology for fabricating valve membranes from silicone rubber. These valve membranes are integrated with other processes on a silicon wafer.
Silicone rubber is rubber made from silicone elastomers. This material has multiple desirable mechanical properties. The inventors found that silicone rubber exhibits a very low modulus of about 1 MPA, good compatibility with IC processes, high elongation, and good sealing properties on rough surfaces.
Small membranes fabricated with silicone rubber can be deflected with a minimum of force. This property results in reduced dead volume and lower power operation of the valve. In addition, due to the high elongation, it is possible to make actuators with millimeter scale vertical displacement
The preferred material is MRTV1(trademark) (produced by American Safety Technologies(trademark)). This material has high elongation and low durometer which results in good sealing. An integrated normally open valve using a silicone rubber membrane and 3M(trademark)PF5060(trademark) liquid for thermopneumatic actuation has been fabricated. For an air flow of about 1.3 1pm, about 280 mW is required to close the valve at an inlet pressure of about 20 psi.